Streptomyces cyaneus dermatitis in a dog

A nearly 4-year-old neutered male Australian Terrier was referred for a nodular pyogranulomatous mass of the right axilla. It had been poorly responsive to antibiotic therapy.

Based on filamentous Gram-positive organisms identified in earlier biopsy material, infection by an Actinomyces sp. was suspected and the dog showed clinical improvement on a trial of potentiated sulfonamides. Recurrence 5 months later prompted euthanasia, with Streptomyces cyaneus being cultured and confirmed by genetic sequencing of part of the 16 s ribosomal RNA gene.

Invasive Streptomyces spp. infections are uncommon in humans and animals, and isolations are sometimes considered to be contaminants, but the demonstration of the organism within the lesion in this instance indicates that the isolation of a Streptomyces sp. from veterinary cases should not always be considered as contamination, because this genus is clearly pathogenic.